Simple Mail Transfer Protocol (SMTP) Enhanced Status Codes Registry2008-05-292015-07-02Class Sub-CodesSpecification RequiredChris Newman2.XXX.YYYSuccessSuccess specifies that the DSN is reporting a
positive delivery action. Detail sub-codes may
provide notification of transformations required for
delivery. (Standards track)G. VaudreuilIESG4.XXX.YYYPersistent Transient FailureA persistent transient failure is one in which the
message as sent is valid, but persistence of some
temporary condition has caused abandonment or delay of
attempts to send the message. If this code accompanies
a delivery failure report, sending in the future may be
successful. (Standards track)G. VaudreuilIESG5.XXX.YYYPermanent FailureA permanent failure is one which is not likely to be
resolved by resending the message in the current form.
Some change to the message or the destination must be
made for successful delivery. (Standards track)G. VaudreuilIESGSubject Sub-CodesSpecification RequiredChris NewmanX.0.YYYOther or Undefined StatusThere is no additional subject information available. (Standards track)G. VaudreuilIESGX.1.YYYAddressing StatusThe address status reports on the originator or
destination address. It may include address syntax or
validity. These errors can generally be corrected by
the sender and retried. (Standards track)G. VaudreuilIESGX.2.YYYMailbox StatusMailbox status indicates that something having to do
with the mailbox has caused this DSN. Mailbox issues are
assumed to be under the general control of the recipient. (Standards track)G. VaudreuilIESGX.3.YYYMail System StatusMail system status indicates that something having to do
with the destination system has caused this DSN. System
issues are assumed to be under the general control of the
destination system administrator. (Standards track)G. VaudreuilIESGX.4.YYYNetwork and Routing StatusThe networking or routing codes report status about the
delivery system itself. These system components include
any necessary infrastructure such as directory and routing
services. Network issues are assumed to be under the
control of the destination or intermediate system
administrator. (Standards track)G. VaudreuilIESGX.5.YYYMail Delivery Protocol StatusThe mail delivery protocol status codes report failures
involving the message delivery protocol. These failures
include the full range of problems resulting from
implementation errors or an unreliable connection. (Standards track)G. VaudreuilIESGX.6.YYYMessage Content or Media StatusThe message content or media status codes report failures
involving the content of the message. These codes report
failures due to translation, transcoding, or otherwise
unsupported message media. Message content or media
issues are under the control of both the sender and the
receiver, both of which must support a common set of
supported content-types. (Standards track)G. VaudreuilIESGX.7.YYYSecurity or Policy StatusThe security or policy status codes report failures
involving policies such as per-recipient or per-host
filtering and cryptographic operations. Security and
policy status issues are assumed to be under the control
of either or both the sender and recipient. Both the
sender and recipient must permit the exchange of messages
and arrange the exchange of necessary keys and
certificates for cryptographic operations. (Standards track)G. VaudreuilIESGEnumerated Status CodesSpecification RequiredChris NewmanX.0.0Other undefined StatusAnyOther undefined status is the only undefined error code.
It should be used for all errors for which only the class
of the error is known. (Standards Track)G. VaudreuilIESGX.1.0Other address statusNot givenSomething about the address specified in the message
caused this DSN. (Standards Track)G. VaudreuilIESGX.1.1Bad destination mailbox address451, 550The mailbox specified in the address does not exist.
For Internet mail names, this means the address portion to
the left of the "@" sign is invalid. This code is only
useful for permanent failures. (Standards Track)G. VaudreuilIESGX.1.2Bad destination system addressNot givenThe destination system specified in the address does not
exist or is incapable of accepting mail. For Internet mail
names, this means the address portion to the right of the "@"
is invalid for mail. This code is only useful for permanent
failures. (Standards Track)G. VaudreuilIESGX.1.3Bad destination mailbox address syntax501The destination address was syntactically invalid. This can
apply to any field in the address. This code is only useful
for permanent failures. (Standards Track)G. VaudreuilIESGX.1.4Destination mailbox address ambiguousNot givenThe mailbox address as specified matches one or more
recipients on the destination system. This may result if a
heuristic address mapping algorithm is used to map the
specified address to a local mailbox name. (Standards Track)G. VaudreuilIESGX.1.5Destination address valid250This mailbox address as specified was valid. This status code
should be used for positive delivery reports. (Standards Track)G. VaudreuilIESGX.1.6Destination mailbox has moved, No forwarding addressNot givenThe mailbox address provided was at one time valid, but mail is
no longer being accepted for that address. This code is only
useful for permanent failures. (Standards Track)G. VaudreuilIESGX.1.7Bad sender's mailbox address syntaxNot givenThe sender's address was syntactically invalid. This can apply
to any field in the address. (Standards Track)G. VaudreuilIESGX.1.8Bad sender's system address451, 501The sender's system specified in the address does not exist or
is incapable of accepting return mail. For domain names, this
means the address portion to the right of the "@" is invalid
for mail. (Standards Track)G. VaudreuilIESGX.1.9Message relayed to non-compliant mailerNot givenThe mailbox address specified was valid, but the message has
been relayed to a system that does not speak this protocol; no
further information can be provided. (Standards Track)E. AllmanIESGX.1.10Recipient address has null MX556This status code is returned when the associated
address is marked as invalid using a null MX. (Standards Track); (Standards Track)J. Levine, M. Delany, J. KlensinIESGX.2.0Other or undefined mailbox statusNot givenThe mailbox exists, but something about the destination mailbox
has caused the sending of this DSN. (Standards Track)G. VaudreuilIESGX.2.1Mailbox disabled, not accepting messagesNot givenThe mailbox exists, but is not accepting messages. This may be
a permanent error if the mailbox will never be re-enabled or a
transient error if the mailbox is only temporarily disabled. (Standards Track)G. VaudreuilIESGX.2.2Mailbox full552The mailbox is full because the user has exceeded a per-mailbox
administrative quota or physical capacity. The general
semantics implies that the recipient can delete messages to
make more space available. This code should be used as a
persistent transient failure. (Standards Track)G. VaudreuilIESGX.2.3Message length exceeds administrative limit552A per-mailbox administrative message length limit has been
exceeded. This status code should be used when the per-mailbox
message length limit is less than the general system limit.
This code should be used as a permanent failure. (Standards Track)G. VaudreuilIESGX.2.4Mailing list expansion problem450, 452The mailbox is a mailing list address and the mailing list was
unable to be expanded. This code may represent a permanent
failure or a persistent transient failure. (Standards Track)G. VaudreuilIESGX.3.0Other or undefined mail system status221, 250, 421, 451, 550, 554The destination system exists and normally accepts mail, but
something about the system has caused the generation of this
DSN. (Standards Track)G. VaudreuilIESGX.3.1Mail system full452Mail system storage has been exceeded. The general semantics
imply that the individual recipient may not be able to delete
material to make room for additional messages. This is useful
only as a persistent transient error. (Standards Track)G. VaudreuilIESGX.3.2System not accepting network messages453, 521The host on which the mailbox is resident is not accepting
messages. Examples of such conditions include an imminent
shutdown, excessive load, or system maintenance. This is
useful for both permanent and persistent transient errors. (Standards Track); (Standards Track)G. Vaudreuil, J. KlensinIESGX.3.3System not capable of selected featuresNot givenSelected features specified for the message are not supported
by the destination system. This can occur in gateways when
features from one domain cannot be mapped onto the supported
feature in another. (Standards Track)G. VaudreuilIESGX.3.4Message too big for system552, 554The message is larger than per-message size limit. This limit
may either be for physical or administrative reasons. This is
useful only as a permanent error. (Standards Track)G. VaudreuilIESGX.3.5System incorrectly configuredNot givenThe system is not configured in a manner that will permit it to
accept this message. (Standards Track)G. VaudreuilIESGX.3.6Requested priority was changed250 or 251The message was accepted for relay/delivery, but
the requested priority (possibly the implied default) was not
honoured. The human readable text after the status code
contains the new priority, followed by SP (space) and
explanatory human readable text. (Standards Track)A. MelnikovIESGX.4.0Other or undefined network or routing statusNot givenSomething went wrong with the networking, but it is not clear
what the problem is, or the problem cannot be well expressed
with any of the other provided detail codes. (Standards Track)G. VaudreuilIESGX.4.1No answer from host451The outbound connection attempt was not answered, because
either the remote system was busy, or was unable to take a
call. This is useful only as a persistent transient error. (Standards Track)G. VaudreuilIESGX.4.2Bad connection421The outbound connection was established, but was unable to
complete the message transaction, either because of time-out,
or inadequate connection quality. This is useful only as a
persistent transient error. (Standards Track)G. VaudreuilIESGX.4.3Directory server failure451, 550The network system was unable to forward the message, because a
directory server was unavailable. This is useful only as a
persistent transient error.
The inability to connect to an Internet DNS server is one
example of the directory server failure error. (Standards Track)G. VaudreuilIESGX.4.4Unable to routeNot givenThe mail system was unable to determine the next hop for the
message because the necessary routing information was
unavailable from the directory server. This is useful for both
permanent and persistent transient errors.
A DNS lookup returning only an SOA (Start of Administration)
record for a domain name is one example of the unable to route
error. (Standards Track)G. VaudreuilIESGX.4.5Mail system congestion451The mail system was unable to deliver the message because the
mail system was congested. This is useful only as a persistent
transient error. (Standards Track)G. VaudreuilIESGX.4.6Routing loop detectedNot givenA routing loop caused the message to be forwarded too many
times, either because of incorrect routing tables or a user-
forwarding loop. This is useful only as a persistent transient
error. (Standards Track)G. VaudreuilIESGX.4.7Delivery time expiredNot givenThe message was considered too old by the rejecting system,
either because it remained on that host too long or because the
time-to-live value specified by the sender of the message was
exceeded. If possible, the code for the actual problem found
when delivery was attempted should be returned rather than this
code. (Standards Track)G. VaudreuilIESGX.5.0Other or undefined protocol status220, 250, 251, 252, 253, 451, 452, 454, 458, 459, 501,
502, 503, 554Something was wrong with the protocol necessary to deliver the
message to the next hop and the problem cannot be well
expressed with any of the other provided detail codes. (Standards Track)G. VaudreuilIESGX.5.1Invalid command430, 500, 501, 503, 530, 550, 554, 555A mail transaction protocol command was issued which was either
out of sequence or unsupported. This is useful only as a
permanent error. (Standards Track)G. VaudreuilIESGX.5.2Syntax error500, 501, 502, 550, 555A mail transaction protocol command was issued which could not
be interpreted, either because the syntax was wrong or the
command is unrecognized. This is useful only as a permanent
error. (Standards Track)G. VaudreuilIESGX.5.3Too many recipients451More recipients were specified for the message than could have
been delivered by the protocol. This error should normally
result in the segmentation of the message into two, the
remainder of the recipients to be delivered on a subsequent
delivery attempt. It is included in this list in the event
that such segmentation is not possible. (Standards Track)G. VaudreuilIESGX.5.4Invalid command arguments451, 501, 502, 503, 504, 550, 555A valid mail transaction protocol command was issued with
invalid arguments, either because the arguments were out of
range or represented unrecognized features. This is useful
only as a permanent error. (Standards Track)G. VaudreuilIESGX.5.5Wrong protocol versionNot givenA protocol version mis-match existed which could not be
automatically resolved by the communicating parties. (Standards Track)G. VaudreuilIESGX.5.6Authentication Exchange line is too long500This enhanced status code SHOULD be returned when the server
fails the AUTH command due to the client sending a [BASE64]
response which is longer than the maximum buffer size
available for the currently selected SASL mechanism. This is
useful for both permanent and persistent transient errors. (Standards Track)R. Siemborski, A. MelnikovIESGX.6.0Other or undefined media errorNot givenSomething about the content of a message caused it to be
considered undeliverable and the problem cannot be well
expressed with any of the other provided detail codes. (Standards Track)G. VaudreuilIESGX.6.1Media not supportedNot givenThe media of the message is not supported by either the
delivery protocol or the next system in the forwarding path.
This is useful only as a permanent error. (Standards Track)G. VaudreuilIESGX.6.2Conversion required and prohibitedNot givenThe content of the message must be converted before it can be
delivered and such conversion is not permitted. Such
prohibitions may be the expression of the sender in the message
itself or the policy of the sending host. (Standards Track)G. VaudreuilIESGX.6.3Conversion required but not supported554The message content must be converted in order to be forwarded
but such conversion is not possible or is not practical by a
host in the forwarding path. This condition may result when an
ESMTP gateway supports 8bit transport but is not able to
downgrade the message to 7 bit as required for the next hop. (Standards Track)G. VaudreuilIESGX.6.4Conversion with loss performed250This is a warning sent to the sender when message delivery was
successfully but when the delivery required a conversion in
which some data was lost. This may also be a permanent error
if the sender has indicated that conversion with loss is
prohibited for the message. (Standards Track)G. VaudreuilIESGX.6.5Conversion FailedNot givenA conversion was required but was unsuccessful. This may be
useful as a permanent or persistent temporary notification. (Standards Track)G. VaudreuilIESGX.6.6Message content not available554The message content could not be fetched from a remote system.
This may be useful as a permanent or persistent temporary
notification. (Standards Track)C. NewmanIESGX.6.7Non-ASCII addresses not permitted for that sender/recipient553, 550This indicates the reception of a MAIL or RCPT
command that non-ASCII addresses are not permitted (Standards track)Jiankang YAOima@ietf.orgX.6.8UTF-8 string reply is required,
but not permitted by the SMTP client252, 553, 550This indicates that a reply containing a UTF-8
string is required to show the mailbox name,
but that form of response is not
permitted by the SMTP client. (Standards track)Jiankang YAOima@ietf.orgX.6.9UTF-8 header message cannot be transferred to one or more recipients, so the message must be rejected550This indicates that transaction failed
after the final "." of the DATA command. (Standards track)Jiankang YAOima@ietf.orgX.6.10This is a duplicate of X.6.8 and is thus deprecated. (Standards track)X.7.0Other or undefined security status220, 235, 450, 454, 500, 501, 503, 504, 530, 535, 550Something related to security caused the message to be
returned, and the problem cannot be well expressed with any of
the other provided detail codes. This status code may also be
used when the condition cannot be further described because of
security policies in force. (Standards Track)G. VaudreuilIESGX.7.1Delivery not authorized, message refused451, 454, 502, 503, 533, 550, 551The sender is not authorized to send to the destination. This
can be the result of per-host or per-recipient filtering. This
memo does not discuss the merits of any such filtering, but
provides a mechanism to report such. This is useful only as a
permanent error. (Standards Track)G. VaudreuilIESGX.7.2Mailing list expansion prohibited550The sender is not authorized to send a message to the intended
mailing list. This is useful only as a permanent error. (Standards Track)G. VaudreuilIESGX.7.3Security conversion required but not possibleNot givenA conversion from one secure messaging protocol to another was
required for delivery and such conversion was not possible.
This is useful only as a permanent error. (Standards Track)G. VaudreuilIESGX.7.4Security features not supported504A message contained security features such as secure
authentication that could not be supported on the delivery
protocol. This is useful only as a permanent error. (Standards Track)G. VaudreuilIESGX.7.5Cryptographic failureNot givenA transport system otherwise authorized to validate or decrypt
a message in transport was unable to do so because necessary
information such as key was not available or such information
was invalid. (Standards Track)G. VaudreuilIESGX.7.6Cryptographic algorithm not supportedNot givenA transport system otherwise authorized to validate or decrypt
a message was unable to do so because the necessary algorithm
was not supported. (Standards Track)G. VaudreuilIESGX.7.7Message integrity failureNot givenA transport system otherwise authorized to validate a message
was unable to do so because the message was corrupted or
altered. This may be useful as a permanent, transient
persistent, or successful delivery code. (Standards Track)G. VaudreuilIESGX.7.8Authentication credentials invalid535, 554This response to the AUTH command indicates that the authentication
failed due to invalid or insufficient authentication credentials. In
this case, the client SHOULD ask the user to supply new credentials
(such as by presenting a password dialog box). (Standards Track)R. Siemborski, A. MelnikovIESGX.7.9Authentication mechanism is too weak534This response to the AUTH command indicates that the selected
authentication mechanism is weaker than server policy permits for
that user. The client SHOULD retry with a new authentication
mechanism. (Standards Track)R. Siemborski, A. MelnikovIESGX.7.10Encryption Needed523This indicates that external strong privacy layer
is needed in order to use the requested
authentication mechanism. This is primarily
intended for use with clear text authentication
mechanisms. A client which receives this may
activate a security layer such as TLS prior to
authenticating, or attempt to use a stronger
mechanism. (Best current practice)T. Hansen, J. KlensinIESGX.7.11Encryption required for requested authentication mechanism524, 538This response to the AUTH command indicates that the selected
authentication mechanism may only be used when the underlying SMTP
connection is encrypted. Note that this response code is documented
here for historical purposes only. Modern implementations SHOULD NOT
advertise mechanisms that are not permitted due to lack of
encryption, unless an encryption layer of sufficient strength is
currently being employed. (Standards Track)R. Siemborski, A. MelnikovIESGX.7.12A password transition is needed422, 432This response to the AUTH command indicates that the user needs to
transition to the selected authentication mechanism. This is
typically done by authenticating once using the [PLAIN]
authentication mechanism. The selected mechanism SHOULD then work
for authentications in subsequent sessions. (Standards Track)R. Siemborski, A. MelnikovIESGX.7.13User Account Disabled525Sometimes a system administrator will have to
disable a user's account (e.g., due to lack of
payment, abuse, evidence of a break-in attempt,
etc). This error code occurs after a successful
authentication to a disabled account. This
informs the client that the failure is permanent
until the user contacts their system
administrator to get the account re-enabled. It
differs from a generic authentication failure
where the client's best option is to present the
passphrase entry dialog in case the user simply
mistyped their passphrase. (Best current practice)T. Hansen, J. KlensinIESGX.7.14Trust relationship required535, 554The submission server requires a configured trust
relationship with a third-party server in order
to access the message content. This value
replaces the prior use of X.7.8 for this error
condition. thereby updating [RFC4468]. (Best current practice)T. Hansen, J. KlensinIESGX.7.15Priority Level is too low450, 550 (other 4XX or 5XX codes are allowed)The specified priority level is below the lowest
priority acceptable for the receiving SMTP server. This
condition might be temporary, for example the server is
operating in a mode where only higher priority messages are
accepted for transfer and delivery, while lower priority
messages are rejected. (Standards Track)A. MelnikovIESGX.7.16Message is too big for the specified priority552 (other 4XX or 5XX codes are allowed)The message is too big for the specified priority.
This condition might be temporary, for example the server is
operating in a mode where only higher priority messages below
certain size are accepted for transfer and delivery. (Standards Track)A. MelnikovIESGX.7.17Mailbox owner has changed5XXThis status code is returned when a message is received with
a Require-Recipient-Valid-Since field or RRVS extension and the receiving
system is able to determine that the intended recipient mailbox has not
been under continuous ownership since the specified date-time. (Standards Track)M. KucherawyIESGX.7.18Domain owner has changed5XXThis status code is returned when a message is received with
a Require-Recipient-Valid-Since field or RRVS extension and the receiving
system wishes to disclose that the owner of the domain name of the
recipient has changed since the specified date-time. (Standards Track)M. KucherawyIESGX.7.19RRVS test cannot be completed5XXThis status code is returned when a message is
received with a Require-Recipient-Valid-Since
field or RRVS extension and the receiving
system cannot complete the requested
evaluation because the required timestamp was
not recorded. The message originator needs to
decide whether to reissue the message without
RRVS protection. (Standards Track)M. KucherawyIESGX.7.20No passing DKIM signature found550This status code is returned when a message
did not contain any passing DKIM signatures. (This violates the
advice of Section 6.1 of .) (Standards Track); (Standards Track)M. KucherawyIESGX.7.21No acceptable DKIM signature found550This status code is returned when a message
contains one or more passing DKIM signatures,
but none are acceptable. (This violates the
advice of Section 6.1 of .) (Standards Track); (Standards Track)M. KucherawyIESGX.7.22No valid author-matched DKIM signature found550This status code is returned when a message
contains one or more passing DKIM signatures, but none are acceptable because
none have an identifier(s) that matches the author address(es) found in
the From header field. This is a special case of X.7.21. (This violates the
advice of Section 6.1 of .) (Standards Track); (Standards Track)M. KucherawyIESGX.7.23SPF validation failed550This status code is returned when a message
completed an SPF check that produced a "fail" result, contrary to local policy
requirements. Used in place of 5.7.1 as described in Section 8.4 of
. (Standards Track); (Standards Track)M. KucherawyIESGX.7.24SPF validation error451/550This status code is returned when evaluation
of SPF relative to an arriving message resulted in an error. Used in place of
4.4.3 or 5.5.2 as described in Sections 8.6 and 8.7 of
. (Standards Track); (Standards Track)M. KucherawyIESGX.7.25Reverse DNS validation failed550This status code is returned when an SMTP
client's IP address failed a reverse DNS
validation check, contrary to local policy
requirements. (Standards Track); (Standards Track)M. KucherawyIESGX.7.26Multiple authentication checks failed550This status code is returned when a message
failed more than one message authentication
check, contrary to local policy requirements.
The particular mechanisms that failed are not
specified. (Standards Track)M. KucherawyIESGX.7.27Sender address has null MX550This status code is returned when the associated
sender address has a null MX, and the SMTP
receiver is configured to reject mail from such
sender (e.g., because it could not return a DSN). (Standards Track)J. Levine, M. DelanyIESG